Most of the knee replacement designs in current use are of the Condylar Replacement type, where the arthritic joint surfaces are resected and are replaced with metal and plastic surfaces. There are two conflicting requirements in design; first, the desirability for freedom of motion requires relatively low conformity between the femoral and tibial surfaces, while the desirability for low contact stresses on the plastic surface requires high conformity. This conflict similarly applies to the patello-femoral bearing joint.